Researchers at the University of Missouri found Arabidopsis, a small flowering plant similar to cabbage and mustard, could recognize the munching sounds of an invading caterpillar. Upon hearing the hungry insect, the plant released additional mustard oils, a compound caterpillars find unappetizing.
"Previous research has investigated how plants respond to acoustic energy, including music," said lead researcher Heidi Appel. "However, our work is the first example of how plants respond to an ecologically relevant vibration."
"We found that feeding vibrations signal changes in the plant cells' metabolism, creating more defensive chemicals that can repel attacks from caterpillars," Appel added.
Previous studies have shown some of the ways plants respond to touch and even wind. But this new study, published in Oecologia, showed the plants were selective in which sounds they paid attention to. Only when caterpillar munching vibrations were recorded and played back for the plants, did they excrete additional mustard oil -- not so for recordings of wind and other vibrations.
"This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration," explained study co-author Rex Cocroft said.
The researchers say better understanding how plants detect and respond to ecological threats could help botanists design plants with improved defense mechanisms.
"Once you understand these things you can mess around with it in plant breeding through conventional methods or biotech approaches to modify plants so they are more responsive in the ways you want to make them more resistant against pests," Appel said. "That's the practical application one day."
Researchers also want to figure out exactly how the plant senses vibrations. That remains a mystery, though Appel and Cocroft guess a protein called mechanoreceptors, which can respond to pressure or distortion, likely plays an important role in the process.
"Finding that out is our next step," said Appel.